System and method for controlling the flow of a gaseous medium through a fluid

ABSTRACT

A method and system for controlling the flow of a gaseous medium through a fluid are described. The method includes providing a rheologic fluid through which a gaseous medium can be conducted, and controlling the viscosity of the rheologic fluid to control the flow of the gaseous medium. The system has a rheologic fluid, which is located in particular in a device to be controlled, a guide guiding the gaseous medium through the fluid, and a field applier for applying a field at least partially in the area of the rheologic fluid.

This application claims the priority of German application 198 16 208.1,filed in Germany Apr. 9, 1998, the disclosure of which is expresslyincorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a method and device for controlling theflow of a gaseous medium through a fluid and/or a device. The presentinvention also relates to the use of a rheologic fluid for variouspneumatic applications.

General information concerning rheologic fluids can be found in “AnIntroduction to Rheology” by H. A. Barnes, J. F. Hutton, and K. Walters,1989. Also, see U.S. Pat. Nos. 2,417,550 and 2,575,360 for a descriptionof magnetic rheologic effects fluids.

Rheologic fluids, particularly magnetorheologic and electrorheologicfluids, the latter alternatively being known as electroviscous fluids,have interesting properties. These interesting properties include inparticular the fact that when a magnetic field is applied to amagnetorheologic fluid and an electrical field is applied to anelectrorheologic fluid, a fluid-solid phase transition takes place.Typically a magnetic field on the order of magnitude of approximately 1kG or an electrical field on the order of magnitude of 1 kV/mm for sucha fluid or such a suspension to become solidified is required. Thismeans that the suspension or fluid has a finite flow (plasticity) limitin the field so that each process that occurs is reversible and thedegree of fluidity of the suspension or fluid can be intentionallyadjusted by changing the strength of the external electrical or magneticfield. The term “fluid” below will be understood to cover liquids andsuspensions.

One advantage of an electrorheologic fluid is that the fluids areessentially insulators, so that the power draw is relatively small.Adaptive bumpers and clutches for motor vehicles, for example, can bemade with rheologic fluids. Such applications are made possible by thefact that the solidification process takes place on a time scale ofapproximately 10⁻³ to 10⁻² seconds.

Possible electroviscous fluids for example are a mixture ofapproximately 40 to 60 wt. % silicic acid as the solid, 30 to 50 wt. %of a suitable organic phase with a low electric constant, 5 to 10 wt. %water, and 5 wt. % of a dispersing agent, which have a basic viscosityof 100 to 3000 nPa.s and a mixture with 50 to 60 wt. % of a siliciticacid, 30 to 50 wt. % of an organic phase with a low boiling point, 10 to50 wt. % water, and 5 wt. % of a dispersing agent such as isododecane.

European Patent 0 222 350 teaches an air spring element in which thespring body is disposed inside a chamber enclosed by a rubber-elasticperipheral wall and two rigid end walls, with the external chamberbetween the spring body and the peripheral wall, said chamber beingdivided by the spring body, being filled with an electroviscous liquidcontrollable by an electrical field.

Unpublished European disclosure 0 590 808 teaches a clutch for a motorvehicle, in which two parts are rotatably connected with each other.These parts move during rotation partially by an electroviscous liquidand a correspondingly greater or lesser coupling of the two parts iscontrolled by the application of a voltage.

The common feature of these two known applications is that theelectrorheologic fluids are used as power transfer media. This has thedrawback that the mechanical components, which are frequently made ofmetal for example, are exposed to the aggressive, particularly chemical,influences of the rheologic fluids. Also, no application can be derivedfrom these two known applications that uses the rheologic fluid,particularly the electroviscous liquid, as a non-power-transferringmedium.

Accordingly, the present invention relates to the use of a rheologicfluid as a non-power-transferring medium with in particular anymechanical components not being exposed to the aggressive, in particularchemical, influences of the fluid. Another goal of the present inventionis to provide a method and a device for controlling the flow of agaseous medium through a fluid and uses of a rheologic fluid wherein, inparticular, the rheologic fluid is not used as a power-transferringmedium and in particular the relatively small yield stress of therheologic fluid has a non-disadvantageous effect.

These goals are achieved according to preferred embodiments of theinvention by providing a system and a method for controlling the flow ofa gaseous medium through a fluid which has the following method steps:

provision of a rheologic fluid through which the gaseous medium can beconducted, and

controlling the viscosity of the rheologic fluid.

These features use advantageous properties of rheologic fluids,particularly the property of a rheologic fluid that its degree ofviscosity or fluidity can be intentionally changed. This intentionalchange is based on the microscopic mechanism of the field-inducedsolidification of the fluid, for which there are various theoreticalmodels in which for example induced dipolar forces or the properties ofwater bridges play an important role. Here, the previously isotropicmaterial becomes strongly anisotropic when a field or for exampleexternal (dynamic) shear forces is/are applied. When an electrical fieldfor example is applied, chains are formed under certain circumstancesthat are preferably oriented in the direction of the external field.

Preferably, the rheologic fluid is an electrorheologic fluid and/or amagnetorheologic fluid. This makes it particularly easy to change theproperties of the fluid. Also preferably the viscosity of the fluid iscontrolled by applying a controllable field. This simplifies controllingthe viscosity of the fluid.

Advantageously, the controllable field is an electrical, magnetic,and/or electromagnetic field. This can be either static or dynamic.

Also preferably the gaseous medium is air, which advantageously makes anumber of pneumatic applications possible at low cost.

According to the invention, a rheologic fluid is used for controllingthe flow of a gaseous medium by the fluid. Preferably, the rheologicfluid in this case is an electrorheologic and/or a magnetorheologicfluid, which simplifies its use for various applications.

According to the invention, a device for controlling the flow of agaseous medium through a fluid and/or through a device is characterizedby

a rheologic fluid, which is located in particular in the device,

a means of guiding the gaseous medium through the fluid, and

a means for applying a field at least partially in the area of therheologic fluid.

Preferably, the rheologic fluid is an electrorheologic and/ormagnetorheologic fluid. In particular in this case the field canpreferably be an electrical, magnetic, and/or electromagnetic field andpreferably the means for applying a field can have electrical and/ormagnetic and/or electromagnetic components. Such components are forexample electrically conducting wires, electrically conducting plates,capacitors, or electromagnets, and, since the power draw of therheologic fluid is relatively low, for example conducting plastics aswell.

Preferably, the gaseous medium is air. This choice leads to for exampleelectropneumatic devices at low cost. If preferably the means of guidingthe gaseous medium are strips, which are located in the device and atleast partially wetted by the fluid, the path of the gaseous medium ismore precisely specified and in particular can be extended, which can inparticular lead to a stronger blockade or slower flow of the gaseousmedium through the fluid.

If preferably the fluid is at a distance from chemically vulnerablematerials, the service life or operating time of such devices isprolonged.

According to certain preferred embodiments of the invention the devicejust described is used as a component for an overpressure valve. In thiscase, the pressure point is preferably set by the strength of the fieldapplied. The higher the field applied, the higher the pressure point. Inparticular, in this application of the device, it must be borne in mindthat the direction in which the field is applied makes a difference forcertain anisotropic rheologic fluids.

According to the invention at least one of the devices described is usedas a component of a control valve. In one application of one of theabove-mentioned devices as a component for a control valve, it ispossible to connect corresponding consumers such as pumps or cylindersfor example.

Advantageously, an overpressure valve is created by one of theabove-described devices, in which a pressure point can be set by thestrength of the field applied.

Also, a control valve is advantageously characterized by at least two ofthe above-described devices, providing an outlet and an inlet for thegaseous medium and connecting the outlet of one of the devices with theinlet of the other device. Preferably, a consumer can be linked to theconnection between the two devices. This measure makes an advantageouselectropneumatic device available.

Advantageously, one of the above-mentioned devices is used for pneumaticcontrol and/or regulation.

In the context of this invention, “control” also means “regulation,”meaning that whenever the term “control” is used in the context of thisinvention, it also covers the meaning of “regulation.”

The invention will now be described without limitation of the generalinventive idea on the basis of embodiments with reference to thedrawings, to which express reference is made as well regarding thedisclosure of all of the details according to the invention that are notexplained in greater detail in the text.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a device for controlling theflow of a gaseous medium through a fluid, constructed according to apreferred embodiment of the invention;

FIG. 1A is a schematic sectional view similar to FIG. 1, showing anotherpreferred embodiment of the invention; and

FIG. 2 is a schematic sectional view of an electropneumatic deviceconstructed according to another preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following figures, identical or corresponding parts are given thesame reference numerals, so they do not have to be re-introduced andonly the differences between these embodiments and the first embodimentwill be explained:

FIG. 1 shows an embodiment according to the invention of a device forcontrolling the flow of a gaseous medium through a fluid 1 and/or adevice 3, shown schematically. In FIG. 1, an electroviscous liquid 1 islocated in a container 3. The electroviscous liquid 1 is enclosed atleast partially by conducting plates 2 or a plate capacitor 2 or thisplate capacitor 2 is disposed outside electroviscous liquid 1 andcontainer 3. A voltage U can be applied to this plate capacitor.

Embodiments in which electrically conducting parts are located insidecontainer 3 and even inside electroviscous liquid 1 are alsocontemplated. In this case, a strip-like arrangement of plate capacitor2 or the conducting parts to which a voltage can be applied iscontemplated.

Gas can be conducted through an inlet 5 through container 3 and henceelectroviscous liquid 1 can be guided to outlet 4, which makes thepressure of the gas at the inlet higher than at the outlet. The gasconducted through, air for example, can be used in this electropneumaticdevice as a power transfer medium. As a preferred embodiment, the devicecan be designed such that the gas first passes through a lamellar spacefilled with the electroviscous liquid, then passes through a region inwhich the gas separates from the liquid, and escapes from the device,and an electrical voltage is applied to this device which causes anelectrical field to be generated in the lamellar space or lamellarcontainer. Because of the above-described behavior of electroviscousliquids in an electrical field, the gas stream that flows through thedevice is influenced.

This device can be called an “electropneumatic transistor” by analogywith a transistor, as pneumatic variations can be brought about bychanging the electrical field.

For example the device according to FIG. 1 can be used directly as anoverpressure valve or as a type of gas pressure throttle. The pressurepoint for a corresponding overpressure valve can be set by appropriatelyadjusting the strips and the strength of the electrical field. Also, thethrottle properties can be controlled and regulated by appropriatelyspecifying the spatial relationships in container 3 and the electricalfields connected to the electroviscous liquid.

FIG. 2 shows a type of control valve in which the two devices accordingto FIG. 1 are in series. Gas for example can flow into inlet 5 andthrough the electroviscous liquid 1 that has had its properties affectedby a voltage U1. Once the gas has been separated from the electroviscousliquid on the right side of container 3, this gas reaches the outlet ofthe container on the left and hence the inlet to a consumer 6 and rightcontainer 3. By applying a second voltage U2 to electroviscous liquid 1,which is in right container 3, it is now possible for example to bringabout a different viscosity or by shaping the lamellar passageways incontainer 3 differently to shape the ability of the gas to flow throughdifferently than in the left container. In this manner, the operation ofconsumer 6 can be controlled. As long as for example the viscosity ofelectroviscous liquid 1 in right container 3 is less than the viscosityof electroviscous liquid 1 in left container 3, the piston of consumer 6can move leftward as shown in FIG. 2. In the reverse case, the piston ofconsumer 6 can move rightward.

In this embodiment a single-acting cylinder 6, returned by a spring notshown in FIG. 2, is preferred. Also it is preferable to provide cylinder6 with ventilation. The ventilating means is also not shown in FIG. 2.

It would also be possible to return the piston without a spring forexample by having the pressure in the feed line to the cylinder be lowerthan the surrounding pressure.

Various structural arrangements can be used to provide for the passageof the gaseous medium, for example air, through the rheologic fluid suchthat the flow of gaseous medium is controlled by the variable viscosityof the rheologic fluid. In a very simple arrangement, the air can passthrough the fluid from underneath to above the fluid by naturalgravitation. The driving force is the temperature of the gas and thefluid, or the so-called brownian fluctuation, together with thegravitation. In embodiments utilizing this phenomena, the fluid isentered from being lost at the inlet of the gaseous medium by way of amembrane which is semipermeable so as to allow the gaseous medium to gothrough the membrane while blocking the flow of the rheologic fluid.

Due to an increase of the brownian motion if the temperature isincreased, the gaseous medium flowthrough can be increased by increasingtemperature. However, the temperature range should be limited as apractical matter because of changes in the rheologic fluid which canreact at high temperatures to the materials in contact with the fluid,and moreover the properties of the rheologic fluid can degrade.

FIG. 1A shows another embodiment according to the invention of a devicefor controlling the flow of a gaseous medium through a fluid and/ordevice, shown schematically. Reference signs 1 a, 2 a, 3 a, 4 a and 5 aof FIG. 1a correspond to reference signs 1-5 of FIG. 1. In addition,however, strips S are disposed in the container 3 a and are at leastpartially wetted with the fluid and serve as means for conducting thegaseous medium.

The physical arrangement for transmitting the gaseous medium, such asair, through the rheologic fluid can also be merely the container itselfin the form of a variable shape. For example, a tube, a cube, arectangular box, a sphere, or other shape could be contemplated, withthe shape being changed by the application of the electrical or magneticfield to the rheologic fluid in contact with the container.

In certain contemplated embodiments, lamella as mentioned above, such asribs or slats, and especially plates, blades or disks which are thin arearranged parallel to one another in the rheologic fluid. Neighboringdisks or plates or other lamella structures can be connected todifferent electrical or magnetic forces so that the control of the fluidintermediate the lamella is improved. For example, if three plates wereused, two of them near walls of opposite sides of a container and one inthe middle and parallel to the other plates, the electric or magneticfield between two neighboring plates could be set such that the fluidbetween those plates selectively closes and opens the passagethroughopening between the plates for the flow of the gas, while on theother side the electric or magnetic field is controlled in such a mannerthat the amount of gas which would come through the fluid is less thanhalf of the highest amount.

A similar arrangement could be formed with four or more plates to form agrid pattern that can be used to control the flow of the gaseous mediumtherethrough by controlling electric or magnetic fields acting on therheologic fluid.

In certain preferred embodiments, the gaseous medium can naturallymigrate through the rheologic fluid when it is in a liquid state, whilesolidification of the rheologic fluid changes the transmission rate ofthe gas.

In certain preferred embodiments, different pressure could be applied atthe inlet and outlet for the gaseous medium, and further controlling theflow through the rheologic fluid by way of the above describedapplication of magnetic or electric fields.

Depending on the amount of gaseous medium which should be fed throughthe fluid, there could be use a cross-flow operation or a dead-endoperation. The above mentioned embodiments all relate to a dead-endoperation. In cross-flow operations, the gaseous medium, or at least alarger amount of the gaseous medium, is fed over the surface of thefluid, and only some parts of the gaseous medium are then migrating intothe fluid and through the fluid. However, the most preferred embodimentsutilize one of the dead-end operations.

A further driving force for the gaseous medium through the rheologicfluid according to certain preferred embodiments is an electrical field.In this case, the molecules or atoms of the gaseous medium areelectrically charged, and an electric field is applied such that thegaseous medium is accelerated in the electric field towards the outlet.In these embodiments, a magnetic rheologic fluid should be utilizedwhich is not affected by the electric field.

According to certain embodiments, to further increase the diffusion ofthe gaseous medium through the rheologic fluid, the gaseous mediumshould be accelerated. A kind of a gas-washing means, a gas-washing pumpor scrubber pump could be utilized for this purpose, as well as theabove-described electrical field application to the gaseous electricallycharged molecules or atoms.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. Method for controlling the flow of a gaseous medium through a fluid, comprising the following method steps: providing an electrorheologic fluid through which the gaseous medium can be conducted, and controlling the viscosity of the electrorheologic fluid to thereby control the flow of the gaseous medium.
 2. Method according to claim 1, wherein the viscosity of the fluid is controlled by applying a controllable field.
 3. Method according to claim 2, wherein the controllable field is an electrical field.
 4. Method according to claim 3, wherein the gaseous medium is air.
 5. Method according to claim 1, wherein the gaseous medium is air.
 6. Method according to claim 1, wherein said electrorheologic fluid is disposed in a control circuit for a device.
 7. Method according to claim 1, wherein said electrorheologic fluid is disposed in a control circuit for an overpressure valve.
 8. Method according to claim 1, wherein said electrorheologic fluid is disposed in at least one control circuit for a control valve.
 9. Method according to claim 8, wherein the at least one control circuit includes at least two control circuits, each of the control circuits being provided with an outlet and an inlet for the gaseous medium and the outlet of one of the control circuits being connected with the inlet of another one of the control circuits.
 10. Method according to claim 1, wherein said electrorheologic fluid is disposed in at least one control circuit for adaptive bumpers for motor vehicles.
 11. Method according to claim 1, wherein said electrorheologic fluid is disposed in at least one control circuit for clutches for motor vehicles.
 12. A system for controlling the flow of a gaseous medium through a fluid comprising: an electrorheologic fluid, a means for guiding the gaseous medium through the fluid, and a means for applying a field at least partially in the area of the electrorheologic fluid.
 13. A system according to claim 12, wherein said fluid is disposed in a control circuit for a device.
 14. System according to claim 12, wherein the gaseous medium is air.
 15. System according to claim 12, wherein the field is an electrical field.
 16. System according to claim 13, wherein the means for conducting the gaseous medium are strips disposed in the device and at least partially wetted with the fluid.
 17. System according to claim 12, wherein the means for applying a field has electrical components.
 18. System according to claim 12, wherein the fluid is at a distance from chemically vulnerable materials.
 19. System according to claim 13, wherein said device is an overpressure valve controlled by said control circuit.
 20. System according to claim 19, wherein a pressure point of the overpressure valve can be set by the strength of the field applied.
 21. System according to claim 13, wherein said device is a control valve controlled by said control circuit.
 22. System according to claim 21, comprising at least two devices being controlled in which an outlet and an inlet for the gaseous medium are provided and in which the outlet of one device is connected with the inlet of the other device.
 23. System according to claim 22, wherein a consumer can be linked to the connection between the two devices.
 24. System according to claim 13, wherein said device is an adaptive bumper for motor vehicles controlled by said control circuit.
 25. System according to claim 13, wherein said device is a clutch for motor vehicles controlled by said control circuit. 